Heater System: Other GMC Envoy I

AUXILIARY HEATER BLOWER SWITCH

A 3-speed blower switch (if equipped) is located on instrument panel, to right of steering column. When switch is in OFF position, auxiliary system does not operate.

BLOWER SPEED SWITCH

The blower speed switch selects low, medium-low, medium-high or high blower speed.

MODE SELECTOR

The mode selector directs discharge air to windshield, floor, or dash outputs, as desired by driver.

TEMPERATURE CONTROL SELECTOR

The temperature control lever or knob controls discharge air temperature in all mode positions. Full hot position provides maximum heat. Full cold position provides unheated air.

OPERATING MODES

Note. To identify heater vacuum selector valve operation at specified modes see scheme 3

VENT Mode

Air is directed to instrument panel outlets.

BI-LEV Mode

Air is directed to instrument panel and floor outlets. A slight amount of air is directed to defroster and side window defogger outlets.

HEAT Mode

Air is diverted to floor outlets to heat passenger compartment. A slight amount of air is directed to windshield and side window defogger outlets.

BLEND Mode

Air is divided between instrument panel and floor outlets, with a slight amount of air going to defroster outlets.

DEF Mode

Air is directed to windshield defroster outlets. A slight amount of air is diverted to floor outlets and side window defogger outlets.

PRELIMINARY CHECKS

Check fuses, fusible links and circuit breakers. Replace as necessary. Ensure harness connectors are tight and free of corrosion. Ensure ground connections are clean and tight. Operate system through all functions to verify problems.

BLOWER OPERATES BUT HEATER DOES NOT SUPPLY HOT AIR

1. Turn ignition on. Using a DVOM, backprobe terminal "B" (Light Blue wire) of heater control module connector C4 to ground. Move temperature control knob from hot setting to cold setting, then from cold setting to hot setting. If voltage varies between about 1-12 volts, go to step 3). If voltage does not vary as specified, go to next step.
2. Check for poor connection at terminal "B" of connector C4. Check Light Blue wire for short to ground or battery voltage. Check for open in Brown wire between heater control module connector C4 and instrument panel fuse block. Repair connections or wiring as necessary. If wiring is good, replace heater control module.
3. Using a DVOM, backprobe temperature door motor terminal No. 10 (Brown wire) to ground. If voltage exists, go to next step. If voltage does not exist, repair open in Brown wire between temperature door motor and instrument panel fuse block.
4. Using a DVOM, backprobe between temperature door motor terminal No. 7 (Black wire) and terminal No. 10 (Brown wire). If battery voltage exists, go to next step. If battery voltage does not exist, repair open in Black wire.
5. Using a DVOM, backprobe temperature door motor terminal No. 8 (Light Blue wire) to ground while moving temperature control knob through all temperature ranges. If voltage varies between 1-12 volts, check for binding of temperature door or poor connections at motor. If connections are good and door does not bind, replace temperature door motor.

HEATER OUTPUT TEMPERATURE CHECK

1. Remove radiator cap when engine is sufficiently cool. Select heater (floor) mode, high temperature setting and high blower speed. Idle engine until coolant can be seen flowing in radiator. Install radiator cap.
2. When engine is warm, after about 20 minutes, drive vehicle at 30 MPH (48 km/h). Measure ambient air temperature and floor outlet air temperature using accurate thermometers. If floor outlet air temperature exceeds minimum specification, heater output temperature is considered sufficient. See «HEATER OUTPUT MINIMUM TEMPERATURE SPECIFICATIONS»(ref-40585-S22351103412001011200000) .

HEATER OUTPUT MINIMUM TEMPERATURE SPECIFICATIONS

Scheme 2

Scheme 3

HEATER CORE

Note. For repair information, see HEATER CORE .

INSTRUMENT PANEL

Note. For repair information, see INSTRUMENT PANEL (I/P) CARRIER REPLACEMENT .